Total Dissolved Solids
Total dissolved solids measures the total concentration of all dissolved substances in pool water, expressed in ppm.
Definition
Total dissolved solids measures the total concentration of all dissolved substances in pool water, expressed in ppm.
Typical Values: Hot tubs: change water when TDS exceeds 1,500 ppm over fill water baseline; Pools: monitor; Salt pools: 3,000–5,000 ppm (salt contributes significantly)
In Plain Language
TDS includes all dissolved salts, chemicals, minerals, and organic compounds. As pool water is used and chemicals are added, TDS increases. High TDS can reduce the effectiveness of sanitisers, interfere with water balance, and contribute to foam in hot tubs. The only way to lower TDS is to drain and replace a portion of the water.
Why It Matters
TDS above 1,500 ppm over baseline (or above 3,000 ppm absolute) in a hot tub is a common trigger for water change. In pools, TDS is less critical but should be monitored.
Typical Values
Hot tubs: change water when TDS exceeds 1,500 ppm over fill water baseline; Pools: monitor; Salt pools: 3,000–5,000 ppm (salt contributes significantly)
Last reviewed: 2026-06-01